Method and system for operating a well treatment chemical pump

ABSTRACT

A method for chemical treatment includes operating a chemical pump having a flow rate capacity of a selected multiple of a flow rate of a chemical required to treat at least one of a well and surface equipment associated therewith. The operating is performed at at least one selected time and for at least one selected duration inversely proportional to the flow rate capacity such that a volume of the chemical pumped in a predetermined time interval substantially equals a required volume of the chemical during the predetermined time interval.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

BACKGROUND

This disclosure relates to the field of chemical pumps used to introducetreatment chemicals into subsurface wells used for production of fluids,e.g., hydrocarbons, from subsurface reservoirs and for injection offluids into such wells, e.g., for disposal of produced fluids such aswater or for maintenance of fluid pressure in a reservoir.

The nature of fluids contained in subsurface reservoirs, combined withconditions of high heat, high fluid pressure, and turbulence to whichthe fluids are often subjected, contribute to the formation anddeposition of contaminants in wells drilled into subsurface reservoirs.Such contaminants include, for example and without limitation, scales,salts, paraffins, and asphaltenes. Salts in water extracted from areservoir, combined with dissolved gases such as carbon dioxide and/orhydrogen sulfide, acidify the extracted water, which then can becomecorrosive to steel piping and equipment disposed in a well and at thesurface.

Bacterial growth is also often present in oil and gas wells. Bacteriagrowth can lead to souring of produced fluids as a result hydrogensulfide formed by metabolic processes of the bacteria. Bacteria can alsoproduce other acids which can lead to corrosive attack to metal pipingand equipment in a well and at the surface.

A number of approaches have been used to inhibit corrosion damage toassets and or remove deposits. For example, in oil and gas production,the technique of “batch treating” is commonly used to reduce corrosion,wherein a slug of a chemical having a selected composition is injectedinto a well at selected time. A typical treatment schedule may compriseone treatment every week or every two weeks, first dispensing into awell a treatment chemical of predetermined volume, followed by aseparate flush treatment, typically water. The foregoing introduction oftreatment chemical and flush may require that fluid production from thewell or injection into the well is stopped and the treatment iscompleted before the well can be returned to its regular operation.Flush fluid is introduced into the well to help disperse the chemicaltreatment to the pipe internal surfaces in the well. The above-describedtreatment/flush process may require a large amount of fluid and suchlarge amounts of fluid can reduce the treated well's fluid producingpotential as a result of increased hydrostatic pressure in the wellcaused by the large volume of introduced fluid. By applying a chemicaltreatment to protect well tubulars (casing and/or production tubing)from corrosion, one may actually be inhibiting the treated well'sfinancial value. In many low pressure gas producing wells, for example,corrosion control batch treatments can cause substantial reductions inoil and gas production volumes for days and even weeks following acorrosion control treatment as described above. In extreme exampleswhere the chemical treatment represents a steep enough economic loss,producers may choose to halt corrosion protection treatment.

Another means of performing chemical treatments is using a processcalled “squeezing”, where a large volume of chemical is introduced intothe reservoir formation such that the treatment chemical binds to theformation rock grains (either chemically or by surface tension) where itis slowly released as fluid is extracted from the formation and movedinto the well to provide a chemical treatment that may remain effectiveover an extended period of time. The cost of using large amounts ofchemical required for squeeze treatment in extended length wells, suchas horizontal wells, could be cost prohibitive. Many such chemicaltreatments require displacement of fluids from the well into theformation with the risk of well damage and/or damage to the permeabilityof the formation and resulting loss of economic value of the well.

In addition to treating wells for corrosion with a batch or squeezetreatment, another method of treating corrosion is to pump chemicalsdirectly into a well tubular, for example in an annular space between aproduction tubing and a well casing. Such treatments are commonlyintroduced into the well through the tubing or casing in wells usingartificial lift (e.g., rod pumps or electric submersible pumps)substantially continuously. Introduction of the treatment chemical maybe either directly into the well at the surface or through a separatecapillary chemical injection line. Continuous chemical injection may bepreferred because treatment chemical is consistently present in thewell.

A limitation to continuous pumped chemical treatment is that thecontinuous operation of the chemical delivery pump puts a lot of wearand tear on the moving parts of the pump and therefore chemicalinjection pumps require frequent maintenance. Also, chemical pumpsoperate within a predetermined window of efficiency of output. There isan optimum effective flow rate range for any given size pump, dischargepressure, and desired fluid flow rate output. A pump designed to movefluid at high rates is not efficient when delivering fluid at relativelylow rates; conversely a pump designed to move fluid at low rates cannotpump large volumes in a short time frame. For example, publishedliterature from Sidewinder Pumps, P.O. Box 80769 Lafayette, La.70598-0769 shows that typical chemical pumps are designed to operatecontinuously, require frequent maintenance, and have a specific optimumoperating range.

Alternative treatment methods have therefore been sought for introducingtreatment agents into oil and/or gas wells as well as flow conduits orother processing equipment used in the production of oil and gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a continuous chemical injection systeminstalled next to a well. Shown in the drawing is a solenoid valve in agas supply line between a pump operating pressurized gas supply and thepump. Also shown is a control box which can be used to control theoperation of the solenoid valve.

DETAILED DESCRIPTION

The present disclosure relates to a method of introducing a chemicaltreatment composition into a well, e.g., into the annular space betweena tubing and casing in the well. The treatment composition may contain aliquid well treatment agent, such as a scale inhibitor, corrosioninhibitor, salt inhibitor, paraffin inhibitor, emulsion breaker, scaleremover or biocide. A treatment method according to the presentdisclosure may be described as a hybrid of those techniques described inthe Background section herein and may be described as a “micro-batch”treatment.

A micro-batch treatment is different than chemical delivery techniquesknown in the art in that treatment chemical is not continuouslyintroduced into the well. In a micro-batch treatment, chemical deliveryfrom a chemical treatment pump is purposely and intentionally startedand stopped. A method according to the present disclosure is similar tobatch treating in that a selected amount or “batch” of treatmentchemical is periodically introduced into a well. The difference betweenmethods according to the present disclosure and batch treatments is thatmethods according to the present disclosure provide more frequentintroduction of treatment chemical into a well, for example, multipletimes a day. The treatment volume in each micro batch treatmentintroduction would be less than that introduced using batch treatment.Individual treatment volumes for a micro batch may range, for example,from a few milliliters to a few pints per treatment, versus a fewgallons in a single batch treatment or drums (e.g., 55 gallon drums) fora squeeze.

Chemical treatments supplied from a continuously operated chemical pumptypically operate 100% or very nearly 100% of the time. Sidewinder Pumps(referenced in the Background section herein) literature states that onemodel of chemical treatment pump can operate over a range of forexample, 5 strokes per minute to 35 strokes per minute continuously.Even though there may be intermittent brief pauses to the operation odsuch pumps, the overall operation of the pump would be consideredcontinuous to those skilled in the art of chemical treatments. Suchchemical treatment pumps are designed and pump displacement volumes arechosen with continuous operation accounted for in the selection.

In many chemical treatment applications a batch treatment is a preferredmethod chemical application. Many oil and gas wells produce smallvolumes of fluid daily and would not require a large amount of chemicalin each treatment. A micro-batch treatment, automatically performed in aselectively controlled manner may be a preferred method. For example, aremotely situated well in a difficult to access area producing 1 barrelper day of bacteria laden water may require a periodic batch treatmentof bactericide. A required bactericide treatment of 1 quart per day inthe water phase of the produced fluid may be required to controlbacterial growth. The volume of water produced may make it uneconomicalto move a treatment truck the distance and endure off road conditions tothe well location to perform a treatment. Also, the low volume ofchemical required may be below the efficient operating parameters of acontinuous operation chemical pump, resulting in an uneconomical excessvolume of treatment chemical introduced into the well and/or surfaceequipment.

A micro batch treatment of chemical supplied over a short time duration,such as a few hours, may be preferred over a slower rate, continuousintroduction of of chemical in some circumstances. Chemical treatmentssuch as bactericide treatments work best by supplying a high dosage ofchemical over a relatively short time duration to result in effectivesterilization. A slower dosage rate of chemical bactericide suppliedcontinuously may not reach a high enough concentration to result ineffective sterilization.

Using a method according to the present disclosure, a switch disposed ina circuit between a power supply and a chemical pump designed forcontinuous operation may be controllably operated such that the chemicalpump does not operate continuously, but when operated, does operate atits designed fluid flow rate. An example of such as switch as applied toa pneumatically operated chemical pump may be a solenoid valve disposedbetween a pressurized gas supply and the pneumatically operated pump.The solenoid valve can be selectively controlled to operate the chemicalpump, wherein the size of the chemical pump is selected to deliverlarger fluid volumes than would be required by the particular well ifthe pump were operated continuously. For example, a chemical pump soldunder the model number Model 84 by Sidewinder Pumps may be made todeliver one quart of treatment chemical in a micro-batch technique.Published literature of the Model 84 pump shows it to be effective in anoperating range of 20 to 120 quarts per day. 20 quarts per day may beobtained by operating the pump at 5 strokes per minute. Even at onestroke per minute, 4 quarts per day is the output of the foregoing pumpand such rate is significantly above the 1 quart per day required forthe above example well. It may be inferred that within the publishedefficient operating rage of such pump it is difficult to deliver a microbatch of one quart per day of treatment chemical to such example wellreliably.

Using a method according to the present disclosure, selectivelyoperating a solenoid valve, such as an Asco brand solenoid valve for 24minutes daily would deliver the proper treatment chemical volume to thewell automatically and reliably. Using the foregoing Sidewinder Model 84pump, one quart per day may be accurately delivered by setting the pumpto operate at 15 strokes per minute, which is within the publishedefficient operating range of the foregoing example pump. If theforegoing example pump were operated at 15 strokes per minute for a fullday (1440 minutes), the total fluid volume output would be 60 quarts.Since the example well described above requires only one quart oftreatment chemical in one day, such volume may be obtained by operatingthe pump 24 minutes continuously, and then stopping operation of thepump for the rest of a 24 hour day.

Methods according to the present disclosure differ from batch treatmentsknown in the art by the manner of delivery. Batch treatments known inthe art are performed with a purposely built truck which is dispatchedto a well at selected times and performs one treatment at each trip tothe well. After the treatment, the truck leaves the well location untilit is time for another treatment. The process is fully manuallyperformed and each treatment is performed one at a time. There is noautomation applied to the process. Methods according to the presentdisclosure automate the treatment process and allow for a fixed locationchemical treatment device to be placed at the well to automatically andeconomically deliver a desired amount of chemical into a well atselected times.

For continuous chemical injection systems known in the art, equipmentused consists of a pneumatic chemical pump, chemical tank, containment,sight glass, hoses and other hardware required to treat an oil and gaswell with a chemical additive. The equipment includes a hose or otherconduit in communication with a high pressure air or gas source and thechemical pump. The air or gas supply is of a suitable pressure anddeliverable volume rate to have the pneumatic chemical pump operatewithin its designed operating parameters. In a method according to thepresent disclosure a controllable valve, such as an electricallyoperated solenoid valve or an electric motor operated valve may bedisposed in the gas conduit between the gas source and the chemicalpump. The air or gas line would be in communication with the chemicalpump when the solenoid or motor valve is open but not in communicationwhen such valve is shut. In the present example embodiment the valve maybe one such as an Asco model HV 4270430001 ¼× 3/32 brass solenoid valve.

Because the valve, whether a solenoid valve or motor operated valve, iselectrically operated, the valve may be operated by a timer or othercontrol device such as a programmable logic controller to selectivelyoperate opening and shutting of the valve. When the solenoid valve isopen, the chemical pump will be in communication with the air or gassupply and the pump will operate within its designed operatingparameters. When the solenoid valve is closed, the air or gas supply tothe chemical pump will be closed, and therefore chemical delivery wouldstop.

Starting and stopping the chemical pump may have several advantages andunique features over having the chemical pump operate continuously. Byselectively and automatically controlling the operation of the pump, thechemical injection rate can be fine-tuned. Many chemical pumps havedifficulty pumping at low rates to treat low production rate wells. Byaltering the output of the pump in a selectively controlled manner, lowinjection rates are possible while maintaining operation of the pumpwithin its designed operating parameters when operating. For example, ifa pneumatic pump can reliably deliver 4 quarts of chemical daily butoperates inefficiently at rates below that, setting the pump output at 4quarts a day and having the pump only operate 1 minute out of every 4minutes or one hour out of every four would effectively deliver 1 quartof chemical daily in a reliable manner.

Continuous functioning of a chemical pump causes excessive wear and tearon many parts of the pump. By minimizing the number of pump strokes thepump makes, less wear and tear is put on the pump. Using the exampleabove, a pump set on an injection rate of 4 quarts per day but onlyoperating 1 minute out of every 4 (or ¼ the total elapsed time) wouldresult in 75% reduction of the operating time of the pump and therefore75% reduction in wear and tear on moving parts. Decreasing the wear andtear and associated maintenance and replaced parts may be an additionalbenefit of a method according to the present disclosure.

FIG. 1 shows a schematic diagram of example parts used for a pneumaticair or gas operated chemical pump using methods according to the presentdisclosure. The example embodiment in FIG. 1 includes additional partsnot ordinarily used in a chemical pump-operated treatment system. InFIG. 1, an electric solenoid valve in the pressurized gas line requiredto make the chemical pump function has been added. Also included is acontrol box which allows for the programming of operation of thesolenoid valve. Programming the functioning of the solenoid valve allowsautomatic control of when the solenoid opens and shuts and the durationof the opening. The control box could be any mechanism used to controlthe functioning of an electric solenoid valve. Examples of such devicesmay include, without limitation, a timer or programmable logiccontroller.

The solenoid valve may be a fail open valve or a fail closed valve. Afail open valve is one which is open if no power is supplied to it toallow it to open or shut. A fail closed valve would be one that isclosed when no power is supplied to the solenoid. In the present exampleembodiment, the solenoid valve may be a fail closed valve such as anAsco model HV 4270430001 ¼× 3/32 brass valve.

EXAMPLE

A field installation is provided herein as an example. A chemicalinjection system was set up on a pumping well near Caldwell, Texas whichhad a low pressure annulus. The objective of the field installation wasto determine if a pneumatic chemical pump could be made to deliverreliably 1 quart per day liquid output. There are numerous wells in thegeographic area of the field installation which produce low fluidvolumes, so a low chemical pump output is desirable. Chemical pumpsknown in the art, however, are not reliable over time at delivering aquart of liquid per day. A prototype chemical delivery system wasdeveloped. A regular industry standard continuous injection chemicaldelivery system was built which included the additional equipment of aprogrammable electric solenoid valve in the gas supply line between thepump and the gas supply source. A control box with power supplied from asolar panel and rechargeable 12 volt battery was included to control theoperation of the solenoid. Pictures of the prototype system are includedseparately.

FIG. 1 shows a schematic of the parts of an embodiment of a chemicalpump system that may operate according to the present disclosure. Achemical tank or reservoir, sight glass, hoses and fittings 1 were setup to treat a pumping well 20 with a low pressure annulus 7 using acorrosion inhibitor treatment chemical. The chemical tank 1 outlet maybe connected to a manually controlled valve 2. The manually controlledvalve 2 may be provided to avoid spillage or loss of chemical duringservicing of the system. The manually controlled valve 2 may beconnected to the suction side of a chemical pump 6, in the presentexample a pneumatically operated, positive displacement chemical pump.An injection rate of one quart of treatment chemical per day was adesired chemical output. The chemical pump 6 is designed to deliver 7quarts per day under full speed continuous injection.

A selectively operated (e.g., Asco model HV 4270430001 ¼× 3/32 brasssolenoid valve) valve 4 may be placed in the gas supply line between agas supply source 3 and the chemical pump 6. A controller 5, forexample, containing a programmable logic controller was programmed tooperate the valve 4 at selected times. The valve 4 was operated to openand supply gas from the source 3 to the chemical pump 6 for 7½ minutesevery 3 hours. Chemical outputs were measured periodically and it wasdetermined the chemical pump output was 150 milliliters every 7½ minutecycle. Every three hours 150 milliliters of chemical was introduced intothe well 20 in a micro-batch fashion. An output of 0.3 gallons per dayor just over a quart per day was the daily output. Modifying the timesequence or frequency or operating the valve 4 could further optimizethe chemical output. The result of the prototype equipment and the fieldexample showed that a selectively operated solenoid using a programmablelogic controller could control the chemical delivery volumes of apneumatic pump.

Other components of the system may include a chemical supply line 6Athat may be coupled to a casing valve 7 on a wellhead 8 affixed to thetop of the well 20. The casing valve 7 is opened into the annular space9 between the well casing 12 and a production tubing 10. The productiontubing 10 may be sealingly seated in the wellhead 8 and have a wingvalve 11 or other fluid control valve in a flow line 13 that dischargesproduced fluid from the well. In some embodiments, the chemical supplyline 6A may be in hydraulic communication with the flow line 13, and/orfluid processing equipment (not shown) disposed at the surface andconnected to the flow line 13.

In some embodiments, the chemical pump 6 may have a rated flow capacityat least four times the required treatment chemical flow rate into thewell 20. The valve 4 may be operated such that the chemical pump 6operates only ¼ of the total time in any selected time interval, e.g.,24 hours. In some embodiments, the chemical pump 6 may have a rated flowcapacity of at least 10 times the required treatment chemical flow rateinto the well 20. The valve 4 in such embodiments may be operated 1/10of the total time. Expressed more generally, the chemical pump 6 mayhave a designed flow rate capacity that is a selected multiple of therequired flow rate of treatment chemical, and the pump 6 is operated foran inversely proportional fraction of the total time to provide therequired flow rate of treatment chemical into a well or into productionequipment in fluid communication with a fluid outlet of a well.

It will be appreciated by those skilled in the art that a pneumaticallyoperated chemical pump is only one example of a chemical pump that maybe used in accordance with the present disclosure. In other embodiments,the chemical pump 6 may be an hydraulically operated pump in fluidcommunication with its drive side to a source of pressurized hydraulicfluid. The hydraulic fluid may be pressurized continuously andselectively applied to the drive side of the chemical pump 6 using asolenoid valve as shown in FIG. 1. In other embodiments, a motor used todrive an hydraulic fluid pump (not shown) may be operated for theselected times and selected durations for which the chemical pump 6 isto be operated. In other embodiments, the chemical pump 6 may beoperated by an electric motor. In such embodiments, the control box 5may directly operate the chemical pump 6 and the solenoid valve may beeliminated or substituted by a low pressure check valve to reduce thepossibility of chemical leakage from the tank 1 through the pump 6 andinto the well 20 when the pump is switched off.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. A method for chemical treatment, comprising:operating a chemical pump having a flow rate capacity of a selectedmultiple of a flow rate of a chemical required to treat at least one ofa well and surface equipment associated therewith, the operatingperformed at at least one selected time and for at least one selectedduration inversely proportional to the flow rate capacity such that avolume of the chemical pumped in a predetermined time intervalsubstantially equals a required volume of the chemical during thepredetermined time interval.
 2. The method of claim 1 wherein thechemical pump has a flow rate capacity of at least four times the flowrate of the chemical required to treat the at least one of the well andthe surface equipment.
 3. The method of claim 1 wherein the chemicalpump has a flow rate capacity of at least ten times the flow rate of thechemical required to treat the at least one of the well and the surfaceequipment.
 4. The method of claim 1 wherein the chemical pump comprisesa pneumatically operated pump, and the operating comprises automaticallyopening a valve between a pressurized gas source and the pneumatic pump.5. The method of claim 3 wherein the valve comprises an electricallyoperated solenoid valve.
 6. The method of claim 4 wherein theelectrically operated solenoid valve is controlled by at least one of atimer and a programmable logic controller.
 7. The method of claim 1wherein a chemical output of the chemical pump is connected to anannular space in a well.
 8. The method of claim 1 wherein a chemicaloutput of the chemical pump is connected to a flow conduit in fluidcommunication with an outlet of a well.
 9. A chemical treatment system,comprising: a chemical treatment pump in fluid communication at anoutlet thereof with at least one of a well and surface equipmentconnected to an outlet of a well, the chemical treatment pump having aflow rate capacity of a selected multiple of a flow rate of chemicalrequired to treat the at least one of a well and surface equipment; anda controller connected between a power supply used to operate thechemical treatment pump and the chemical treatment pump, the controllerprogrammed to operate the chemical treatment pump for time intervalsinversely proportional to the selected multiple of the flow rate. 10.The system of claim 9 wherein the controller comprises a valve and thepower supply comprises a pressurized gas source.
 11. The system of claim10 wherein the valve comprises an electrically operated solenoid valve.12. The system of claim 11 wherein the electrically operated solenoidvalve is controlled by at least one of a timer and a programmable logiccontroller.
 13. The system of claim 9 wherein a chemical output of thechemical treatment pump is connected to an annular space in a well. 14.The system of claim 9 wherein a chemical output of the chemicaltreatment pump is connected to a flow conduit in fluid communicationwith an outlet of a well.